[lug] RH Linux download + hdparm

[John Karns]

On Tue, 23 Oct 2001, D. Stimits said:

> John Karns wrote:

> > Thanx for the response.  But I'm not too sure about the gains.  I'm
> > running a U160 drive with an ultra-wide (40 MB/s Tekram 390U) controller
> > on an Asus P5A mobo (33 Mhz PCI, 500Mhz K6-II cpu).  hdparm says I'm
> > getting 15 MB/s.  I had been wanting to order a U160 controller to replace
> > the 390, but under the circomstances, I'm afraid that it could be a waste
> > of $$.  Perhaps I'll try a quick benchmark with an Adaptec 2940UW for
> > comparison to see if it's a controller issue.
>
> If your drive only runs 15 MB/s, you wouldn't have much to gain. The
> exception is if your PCI bus is already bandwidth challenged by some
> form of i/o, then the burst rate would be very helpful. SCSI, unlike
> IDE, is rather intelligent, and you don't generally worry about things
> like DMA settings. On the actual SCSI cable, devices can get
> instructions and then detach until they have something to send back
> (other drives get to work). Thus drive cache ram that can burst quickly,
> and generally small data transfers as well, will grow in benefit as you
> add more scsi drives to a single cable. On the PCI bus end, it has to
> operate at the bus speed, the question then is how well your specific
> controller cooperates with other devices.

I'm mystified.  The drive is a 68-pin Quantum Atlas V with active
termination, rated at 29MB/s, 7200rpm.  Must be the controller or mobo.
The machine is not process bound either (virtually idle), so I doubt that
the bus is i/o bound.  Although it could be a mobo design issue I suppose
- it's showing its age.  It would be interesting to read some performance
specs on those mobos.


> Now if you know for a fact that you are going to use scsi, and buy new
> drives in the future, you might still want to get U160. I say this
> because although controller cards are significantly more expensive, the
> U160 drives of otherwise similar spec to uw or u2w are only a few
> dollars different (and many of the lower end drives are going away).
> Once you absorb the controller cost, drive expense by interface isn't
> that different. And you will never find an uw 10k rpm or 15k rpm, they
> will never be built.

I've always been sold on SCSI - not for i/o speed so much as the gain in
multitasking performance.  I will probably upgrade the mobo before looking
for a U160 controller though.

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John Karns                                        jkarns at csd.net